Classifications

• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B17/00—Monitoring; Testing
  • H04B17/20—Monitoring; Testing of receivers
  • H04B17/21—Monitoring; Testing of receivers for calibration; for correcting measurements
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B17/00—Monitoring; Testing
  • H04B17/10—Monitoring; Testing of transmitters
  • H04B17/11—Monitoring; Testing of transmitters for calibration
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/0202—Channel estimation
  • H04L25/0212—Channel estimation of impulse response
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B17/00—Monitoring; Testing
  • H04B17/10—Monitoring; Testing of transmitters
  • H04B17/11—Monitoring; Testing of transmitters for calibration
  • H04B17/12—Monitoring; Testing of transmitters for calibration of transmit antennas, e.g. of the amplitude or phase
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04B—TRANSMISSION
  • H04B17/00—Monitoring; Testing
  • H04B17/10—Monitoring; Testing of transmitters
  • H04B17/11—Monitoring; Testing of transmitters for calibration
  • H04B17/14—Monitoring; Testing of transmitters for calibration of the whole transmission and reception path, e.g. self-test loop-back
• • H—ELECTRICITY
  • H04—ELECTRIC COMMUNICATION TECHNIQUE
  • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
  • H04L25/00—Baseband systems
  • H04L25/02—Details ; arrangements for supplying electrical power along data transmission lines
  • H04L25/0202—Channel estimation
  • H04L25/024—Channel estimation channel estimation algorithms
  • H04L25/0256—Channel estimation using minimum mean square error criteria

Definitions

• the present invention relates to a wireless communication system, and in particular to a reciprocal error calibration apparatus and a reciprocal error calibration method. Background technique
• Channel reciprocity error is one of the key features of time-division multiplexed TDD systems, which play an important role in most TDD (eg, TD-SCDMA, WiMAX, WiFi, etc.) systems, enabling a variety of advanced signal processing (beamforming) , MIMO, transmit diversity, etc.) were implemented.
• TDD time-division multiplexed
• MIMO massive MIMO
• transmit diversity etc.
• Reciprocal error is reduced by antenna array reciprocal error calibration.
• the technical problem to be solved by the present invention is to provide a calibration method capable of achieving optimum performance.
• the method is robust and accurate, and can be used for advanced processing in TDD systems such as beamforming, MU-MIMO and CoMP.
• a reciprocal error calibration method comprising the steps of: measuring a downlink channel response H D L ; measuring an uplink channel response ⁇ ⁇ ; based on H D and H UL , according to reciprocity
• the algorithm employing the LS criterion is a basic least squares ELS algorithm.
• the algorithm using the MMSE criterion is one of a matrix least squares MLS algorithm and a matrix MMSE algorithm.
• the further algorithm adopting the MMSE criterion is one of a matrix least square MLS algorithm and a matrix MMSE algorithm.
• the method is performed at a user equipment or base station.
• a reciprocal error calibration apparatus comprising: a downlink measurement apparatus that measures a downlink channel response H D L ; an uplink measurement apparatus that measures an uplink channel response ⁇ ⁇ ; LS computing device, based! ! ⁇ And!
• a UE/eNB reciprocal calibration solution for a TDD system is proposed, which can be used for a single cell or CoMP situation.
• the reciprocal error calibration method and the reciprocal error calibration apparatus according to the embodiments of the present invention can provide better reciprocal error calibration capability, and are improved based on The performance of the channel reciprocal TDD system, especially in the SNR area of normal operation
• Figure 1 shows a block diagram of a conventional TDD system equipped with a self-calibrating circuit.
• Figure 2 shows a base station eNB and user equipment in a TDD system that traditionally supports air interface calibration.
• Figure 3 shows a schematic block diagram of a system model in accordance with an embodiment of the present invention.
• FIG. 4 shows a flow chart of a reciprocal error calibration method according to an embodiment of the present invention
• FIG. 5 shows a block diagram of a reciprocal error calibration apparatus according to an embodiment of the present invention
• FIG. 6 shows an embodiment according to the present invention. The simulation results of the reciprocal error calibration method compared with the traditional reciprocal error calibration method. detailed description
• Uplink UL/Downlink DL channel reciprocity is one of the key features of the TDD system.
• the TX/receive RX radio frequency (RF) circuit mismatch in the UE and the eNB, the Doppler asymmetry due to the movement, and the estimation algorithm error between the UE and the eNB result in not always between the UL and the DL.
• the channel is reciprocal. Therefore, antenna array reciprocal error calibration is required to meet the needs of different situations.
• Air Interface Calibration is a software-only calibration that usually does not require any hardware support. More importantly, in distributed antenna systems, air interface calibration does not require absolute reciprocal measurements. Therefore, 3GPP LTE-A is more concerned with OTA calibration.
• Figure 1 shows a block diagram of a conventional TDD system equipped with a self-calibrating circuit.
• TX and RX represent the transmitter and receiver, respectively; CTX and CRX represent the calibration transmitter and calibration receiver, respectively; TR Switch represents the transmit/receive switch; Base Band represents the baseband processing circuit.
• Fig. 1 mainly shows reciprocal calibration on the base station eNB side. The following narrowband variables can be defined:
• it can be selected as the reference reciprocity of the eNB, used as the calibration of the ith antenna.
• FIG. 2 shows a schematic diagram of the structure of a TDD base station eNB and a user equipment UE that conventionally supports over-the-air calibration and calibration signaling between the two.
• TX and RX represent the transmitter and receiver, respectively;
• TR Switch represents the transmit/receive switch.
• the following variables can be defined: : Measurement response of the emission calibration loop of the ith antenna
• the reference reciprocity of the eNB can be selected as the reference reciprocity of the eNB, and is used as the calibration weight of the ith antenna.
• distributed antenna systems such as Coordinated Multi-Point Processing (CoMP) systems
• CoMP Coordinated Multi-Point Processing
• the traditional self-calibration method cannot be used.
• improved self-calibration or air interface calibration with auxiliary backhaul signaling can be used (see [3]).
• TDD CoMP For the traditional calibration technology solution of TDD CoMP, it should be in the eNB to eNB link (for example, X.2)
• a logical channel is allocated on the link to transmit global reference reciprocity.
• this global reference can be an absolute reciprocity of a calibrated TX response / RX response.
• the global reference may be the measurement reciprocity of any antenna branch of the eNB participating in the calibration (see [3]).
• the air interface calibration is for a system of concentrated antenna arrays.
• the new technology can be directly extended to a self-calibration scenario of a distributed over-the-air calibration system or a centralized or distributed antenna array system, for example, by treating the calibration transceiver as a UE and the hardware calibration network as an air interface channel, And exchange global benchmarks over the backhaul link as needed.
• the eNB For air interface reciprocal calibration, the eNB is responsible for collecting uplink and downlink channel measurements and calculating reciprocal calibration weights, typically due to hardware advantages relative to the UE. Next, it is assumed that a calibration operation is performed in the eNB. This does not mean that the possibility of performing calibration at the UE is ruled out (see [4]). The present invention is equally applicable in the scenario where the UE performs calibration.
• Literature [1] and [2] describe a centralized self-calibration technique for different systems.
• Literature [3] proposes an air interface calibration technology solution for LTE and LTE-A systems.
• the downlink channel reciprocity error is estimated by the measured uplink channel reciprocity error, or the uplink channel reciprocity error is estimated by the measured downlink channel reciprocity error.
• the basic idea adopted is the same. That is, based on simple dot-division, the goal is to ensure a least square LS (Least-Square) error.
• the advantage of the algorithm using the least squares LS criterion is that the calculation is simple, but the algorithm cannot achieve optimal performance because the square estimation error causes loss of system performance.
• the reciprocity error between the UE and the eNB side should be calibrated at the same time.
• the basic idea of the present invention is to estimate the reciprocity error using a better-precision algorithm after calculating the reciprocally calibrated channel response of the uplink (downstream) channel according to a known calibration algorithm (e.g., an algorithm using the LS criterion).
• the idea of the present invention can be applied to both air interface calibration and self-calibration.
• the better criterion may be a minimum mean square error MMSE criterion
• the algorithm using the better criterion may be, for example, a matrix least squares (MLS) algorithm and a matrix MMSE algorithm.
• MLS matrix least squares
• a more practical reciprocal error calibration process in accordance with an embodiment of the present invention is described below based on a model of [3GPP RANI Tdoc for LTE and LTE-A, Rl-09462 '2].
• Figure 3 shows a schematic block diagram of a system model in accordance with an embodiment of the present invention.
• a wireless transmitter has a different RF circuit than a wireless receiver. It is assumed that the coupling effect between the antennas is very small compared to the response of the antenna unit itself.
• the effective channel response of the RF channel H E ⁇ H ⁇ , H 6I , H ⁇ H M ( ⁇ can be constructed as a matrix of '' characteristics, for example:
• the actual channel downlink and uplink through which the signal passes are:
• Equation (5) provides a reciprocal model between the actual downlink and downlink channels.
• the purpose of the reciprocal error calibration is to calculate the reciprocity error on the eNB side and the reciprocity error E " on the UE side according to the pilot signal, and use it to compensate the user signal for use in estimating To ensure the reciprocity of H fli and vice versa.
• the reference channel signaling such as the downlink channel state information reference signal CSI-RS and the uplink reference signal SRS in LTE-A, can be measured and H .
• H D E m lH ⁇ E , where two independent because matrix E ⁇ and unknown, which is apparently not directly solved.
• the multi-parameter estimation problem is expressed by a mathematical formula, and the correlation with the 1 ⁇ estimate is eliminated to minimize the minimum mean square error MMSE, instead of minimizing the least squares LS error as in the above literature.
• ⁇ , ⁇ , + ⁇ respectively represent the sum of the downlink and uplink channel response sums, with error coefficient squared matrices A', B', and complex Gaussian white noise AWGN, respectively Noise N ⁇ and N
• a ', AB are full rank matrices, and by substituting the reciprocity model (5) into equation (6), the hypothesis can be obtained.
• N is a matrix whose elements satisfy the independent complex Gaussian distribution ⁇ (0, ⁇ ).
• the basic least squares ELS (literature [4]) estimation algorithm can be used to estimate 1 ⁇ first (using the hypothesis (4) ), equivalent to E's estimate), to eliminate the association between E and E estimates.
• ⁇ [] represents a diagonal transformation
• the advantage of the MMSE-based estimation algorithm over the ELS algorithm in the literature [4] is that it does not require the assumption that 3) is established, so it is more in line with the actual situation and can provide better reciprocal error calibration performance.
• Matrix LS (least square) estimation method is shown. Depending on the design needs (the trade-off between complexity and performance), other variants can be implemented by reference to [J. Proakis, "Digital Communications", McGraw-Hill Science, 4 edition, August 15, 2000]. Matrix LS (least square) estimation method:
• FIG. 4 shows a flow chart of a reciprocal error calibration method in accordance with an embodiment of the present invention.
• step S101 the UE measures the downlink channel response from all its antennas and feeds the measured feedback to the eNB.
• the measured ⁇ can be fed back to the eNB through channel state information (CSI).
• CSI channel state information
• step S102 the eNB measures an uplink channel response ⁇ according to an uplink reference signal (SRS).
• SRS uplink reference signal
• E.g., eNB can Using the ELS algorithm, according to the above formula (6) ⁇ (8), the reciprocal error E Tha of the user equipment is calculated.
• step S104 the eNB calculates another one of £ and ⁇ according to one of the calculated E réelle and ⁇ using another algorithm employing the MMSE criterion. For example, as described above, the eNB calculates the reciprocity error E 4 of the base station according to the calculated reciprocity error of the user equipment by using the matrix LS algorithm or the matrix MMSE algorithm.
• Figure 5 shows a block diagram of a reciprocal error calibration apparatus in accordance with an embodiment of the present invention.
• the reciprocal error calibration method and the reciprocal error calibration apparatus according to an embodiment of the present invention described in conjunction with Figs. 4 and 5 are shown as being implemented at the eNB. Those skilled in the art will recognize that the present invention is not limited thereto.
• the reciprocal error calibration method and the reciprocal error calibration apparatus according to an embodiment of the present invention can also be implemented at the UE.
• the downlink measurement device 101 can be arranged at the UE.
• the reciprocal error calibration apparatus further includes a transmitting apparatus at the UE, configured to transmit a downlink channel response measured by the UE from all of its antennas to the eNB; and at the eNB And a receiving device, configured to receive a downlink channel response ⁇ from the UE.
• a transmitting apparatus at the UE configured to transmit a downlink channel response measured by the UE from all of its antennas to the eNB; and at the eNB And a receiving device, configured to receive a downlink channel response ⁇ from the UE.
• the parameters used in the simulation are as follows: LTA-A link, 3 UEs, 3 eNBs, each UE has 2 antennas, each eNB has 4 antennas, adopts 16QAM, Turbo code, Imps rate, Urban macro cell scene , -5dB inter-cell interference, 6-bit channel quantization for feedback.
• Figure 6 shows simulation results comparing a reciprocal error calibration method with a conventional reciprocal error calibration method in accordance with an embodiment of the present invention.
• the signal to interference plus noise ratio (SINR) of the demodulator input signal is used as a performance metric.
• This metric can be mapped to BER/BLER by looking up the input/output SNR map of the 16QAM+Turbo code.
• SRS w/o RE indicates the channel measurement result without reciprocity error
• ELS eNB + UE Cal indicates the channel measurement result of the reciprocal error calibration of the ELS estimation algorithm of the base station and the terminal simultaneously
• LS eNB Cal indicates that channel measurement results for LS reciprocal error calibration only for eNB are applied
• RE w/o Cal indicates that channel measurement results without reciprocal error calibration are applied
• MLS eNB + UE Cal indicates that the application is based on The invention simultaneously performs the channel measurement result of the reciprocal error calibration of the MLS estimation algorithm of the base station and the terminal
• MMSE eNB+UE Cal indicates that the reciprocity error of the MMSE estimation algorithm of the base station and the terminal is simultaneously applied according to the present invention. Calibrated channel measurements.
• the MMSE estimation algorithm on the eNB side can achieve near-perfect performance, especially in the operating SNR range (0dB-20dB).
• the iterative estimation of the reciprocal error on the UE side and the reciprocity error on the eNB side may be performed according to the foregoing model.
• an ELS estimation algorithm can be used to estimate ⁇ , then an MMSE estimation algorithm is used to estimate ⁇ , and then updated using a matrix MMSE estimation algorithm.
• the process can also be initiated from the ELS estimation algorithm, ie using an ELS estimation algorithm, then estimating using an MMSE estimation algorithm, and then updating the E * using a matrix MMSE estimation algorithm.
• the present invention proposes a UE/eNB reciprocal calibration solution for a TDD system that can be used in a single cell or CoMP scenario. Improved performance of TDD systems based on channel reciprocity, especially in the SNR region of normal operation.
• the functions implemented by the base station proposed by the embodiment of the present invention are described above in the form of method steps, each step shown in FIG. 4 may use one or more of the functions shown in FIG. 5 in practical applications. Module implementation. The functional modules can also be integrated in a chip or a device in practical applications. It will be understood by one of ordinary skill in the art that the base station in the embodiments of the present invention may also include any unit or device for other purposes.
• some embodiments also include a machine readable or computer readable program storage device (eg, a digital data storage medium) and encoding machine executable or computer executable program instructions, wherein the instructions perform some of the above methods or All steps.
• the program storage device can be a digital memory, a magnetic storage medium (such as a magnetic disk and magnetic tape), a hardware or an optically readable digital data storage medium.
• Embodiments also include a programming computer that performs the steps of the above method.

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• Computer Networks & Wireless Communication (AREA)
• Signal Processing (AREA)
• Physics & Mathematics (AREA)
• Electromagnetism (AREA)
• Power Engineering (AREA)
• Mobile Radio Communication Systems (AREA)
• Monitoring And Testing Of Transmission In General (AREA)

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• 2010
  • 2010-10-12 BR BR112012020140A patent/BR112012020140A2/pt not_active IP Right Cessation
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  • 2010-10-12 EP EP10845459.6A patent/EP2536036A4/en not_active Withdrawn
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  • 2010-10-12 WO PCT/CN2010/001595 patent/WO2011097785A1/zh active Application Filing
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